Image denoising is an important process in ISP processing. There are a variety of image denoising methods. Currently, a majority of the image denoising methods based on median filter are very simple. FIG. 1 illustrates a conventional method for image denoising. For a current pixel, three groups of pixels are selected from its neighboring pixels using a certain approach. Medians Φ1, Φ2 and Φ3 for the three groups of pixels values are calculated, respectively. Denoising is then performed on the current pixel. Edge preserving is conducted if the current pixel is located on the edge.
The denoising effect of the above traditional denoising method is not satisfactory and new noise may be introduced sometimes. This is even more the case when a bad pixel exists in the image.